The present invention is directed to a device for limiting the width of a glue film being applied on a roller which is arranged within a machine which continually produces a stratified web-like workpiece. More specifically, the invention is directed to a device to control the width of the glue film on a glue applying roller which itself is located in a double-face gluing station arranged within a machine the produces corrugated board.
In producing a "double-face" corrugated board, which is two outer sheets joined together by a corrugated inner layer, a first cover sheet paper web travels almost directly through such a double-face gluing station as well as at least a second so-called "single-face" web, which is a corrugated paper glued onto a body paper. In this station, a glue applying or sizing roll will apply a predetermined amount of glue on every crest of the single-face web in such a way that the crest may be assembled with the cover paper web at a level of the so-called double-face station which will include a succession of heating tables as well as a pressure assembly means.
One of the problems caused by the high travelling speed of the cover paper web through the various stations is a lateral shifting of the web which cannot be reduced to a rate lower than more or less than 30 millimeters despite all of the guiding devices. Thus, a systematic gluing over the whole width of the corrugations of the single-face web leads very quickly to a clogging of the heating tables of the double-face station due to the glue application on the uncovered portions of the corrugated parts. This phenomenon is hazardous and will produce two large welts of hardened glue build-up on the table, which residue might strongly damage the edges of the corrugated boards which are later produced.
In order to solve the problem, the glue container in which the gluing roll of the double-face station dip is constructed with variable geometry, i.e., the lateral walls are automatically shifted crosswise according to the instantaneous position of the cover paper web as scanned by an appropriate detecting device. Hence, the position and the width of the glue film gathered by the gluing roll are directly linked with the location of the cover paper web, which means that during the assembling process accomplished in the double-face station, the corrugations not covered by this cover paper web will have no previous application of glue.
Even though this device automatically limits the width of the glue film satisfactorily, it suffers from numerous inconveniences. First of all, it is almost impossible to quickly shift the lateral walls without involving an involuntary change in the level of the resident glue within the container, which change in level might mean an excess or lack of glue on the glue applying roll and then on the crest. In other words, dirt will still build up on the heating tables in the course of too quick of transition or the production of sheet-like corrugated board. Furthermore, the technique of shiftable lateral walls is awkward, especially when it concerns the creation of tight seals between the container and the perimeters of the walls and surface of the glue applying roll. Due to these facts, the devices are rather expensive to manufacture.